Do you have photos of the chick and her poop?
Seeking vet care is always best, we are not vets nor experts here.
Is she were mine, for a chick this young, I'd be inclined to treat for Coccidiosis and sour crop if the crop is like a fluid filled balloon.
I'd direct oral drench her with Corid, this tiny and young, give around 3-4 drops of undiluted Liquid Corid once a day for 3 days.
Give her a few small chick sized chunks of coconut oil and about about an 1/8" of vaginal yeast cream or athlete's foot cream (Miconazole/Clotrimazole), this twice a day for 7 days.
It's a given that you will continue to keep the vent clean, provide a source of heat, etc. etc.
IN ADDITION to the direct drench of Corid, give her mixed Corid for drinking water. If you need to, syringe the mixed water into her, but it's best if she will drink on her own. If she's not drinking really well, the mixed water can also be used to make a wet mash of her feed. It's very hard to overdose Corid.
Liquid Corid dose is 2tsp or Powdered Corid is 1 1/2tsp per gallon of water given as the only source of drinking water.
I know this all sounds like a lot for such a tiny baby, but what we're doing here is treating Coccidiosis, in case this is part of the problem. Coccidiosis can cause inflammation in the intestines which in turn can slow the digestive system, which can cause the crop to be very slow. We're trying to head off sour crop. The cream will help with that. Coconut oil is helpful with yeast, but it may also help if there's a blockage and get things moving.
I've only ever had one chick with similar symptoms, he was a bit older, maybe 3 1/2 wks, but after a couple of days he was much improved. I did finish 7 days with him even when he seemed recovered after around the 5 day mark.
I did also provide mixed Corid water for all the chicks (+the broody) to drink as well. Corid won't hurt your broody nor the other chicks. If they are in a large mixed flock with other adults, then I just treat all the flock's water (won't hurt your other adults). Do make some chick sized grit available for your babies if you don't already.
This is my 2¢ hopefully someone else will chime in with their thoughts/suggestions.